The Cell Physiology Core supports the CF Research Center by providing access to video-enhanced light microscopy and epithelial electrophysiology, not only to researchers directly involved with CF research, but also, to others working on pulmonary research or epithelial electrolyte transport, as these areas are related and also have relevance for CF patients. The imaging facility consists of two complete microscope set-ups with image acquisition, analysis software, data storage, and the appropriate equipment for maintaining live cells (controlled environment and temperature) plus one additional analysis station: 1) an upright Zeiss ACM microscope that is equipped with epifluorescence, an intensified CCD camera and Universal Imaging's 1/FL PC-software. 2) An inverted Zeiss Axiovert 35 microscope with automated filter wheels, stage, and focus, a cooled CCD camera and Macintosh based imaging software from Biological Detection Systems. The electrophysiology facility consists of an incubator and a voltage clamp, also equipped with controlled environment and temperature, and Millicel ERS probes. The video-enhanced light microscopes are used predominantly for dynamic experiments of regulation of intracellular ion concentrations with fluorescent indicator dyes (Ca, Cl, Na, pH), for co-localization of fluorescent tags, e.g., differently labeled antibodies, and for 3-dimensional visualization (3-D reconstruction). The voltage clamp set-up (Ussing chamber) is used for detailed electrophysiological analysis of epithelial cell monolayers on filters or of whole epithelial tissues (in a modified Ussing chamber), and the Millicel ERS probes are used for routine measurements of transepithelial conductance. The Core maintains and improves the instrumentation, provides training and supervision of users in the use of the technologies, also provides quality control and serves as a focus for the exchange of ideas among participating investigators. The Core charges a fee for the use of the imaging facility in order to defray part of the cost of repairing and replacing either worn or outdated equipment of the imaging facility, and to encourage thoughtful utilization of this resource. The availability of the Core not only gives investigators access to technically specialized and expensive instrumentation but allows them to concentrate their efforts on the biological questions of interest rather than on the technical aspects of the instrumentation. The utilization of this Core by the CF Research Center investigators and associates has increased substantially over the past five years as evidenced by the increased number of publications and grant support.